1 Field of the Invention
The present invention relates to an image data processing apparatus related to a liquid ejection apparatus which records an image on a recording medium by ejecting a liquid from a plurality of ejection openings, and a liquid ejection apparatus including the image data processing apparatus.
2 Description of the Related Art
An ink jet head of an ink-jet printer has a plurality of nozzles for ejecting therefrom ink towards a recording medium such as a print sheet. In such an ink jet head, ink in each nozzle is sometimes thickened over time and thereby causes unstable ink ejection characteristics and ejection defects. A known approach to prevent this problem is a preliminary ejection in which ink not contributing to image formation is ejected from the nozzles towards a recording medium for use in an image formation, thus preventing thickening of ink inside the nozzles.